FNAL-E-0715()
Precision Measurement of the Decay $\Sigma^- \to N e^- \nu$
()
- Proposed: Feb 19, 1982,
- Approved: Jun 23, 1982,
- Completed: Feb 14, 1984
Charged Hyperon Collaboration
Uses the apparatus of FNAL-497 augmented by a neutron detector and a double level of electron identification. Ran for 820 hours.
The Charged Hyperon Collaboration was one of the groups using high energy hyperon beams at the Tevatron to study the mechanisms by which hyperons are produced and decay. These three experiments, E715, E761, and E781, shared a largely constant set of, now senior physicists and the the Proton Center charged hyperon beam which was built in the Main Ring era for the original hyperon experiment, E497. A hyperon is a baryon, a relative of the proton, which contains at least one strange quark and decays by the weak interaction. The decays of these particles provide insights into the structure of the baryon family that are inaccessible with other techniques. The fundamental questions are basic: "what are these things made of and how are they put together?" The discovery, by E8 in 1976, that hyperons are produced polarized makes the hyperon beam a sensitive and unique probe for this type of physics. E715, the first experiment to use the Tevatron during its 400 GeV commissioning run in 1983, resolved a long standing and potentially serious anomaly in the beta decay of the S‾ hyperon; S‾® ne‾ n. In four previous measurements, the angular correlation of the electron direction relative to the S‾ spin had the "wrong" sign. If these observations were confirmed, then the decay was either due to a new weak interaction (right handed W's, in the jargon) or the accepted spin structure of the S‾, and by extension the whole baryon family, was just wrong. Never-mind. With 100 times the previous world's data, E715 contradicted the old measurements and got the expected sign and magnitude of the electron correlation. E715 also made precision measurements of the magnetic moments of both the S‾ and X‾, and made significant contributions to the development of transition radiation detectors (TRDs) as high performance electron identifiers.
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